AudioCircle
Other Stuff => Archived Manufacturer Circles => Music Reference => Topic started by: Roger A. Modjeski on 4 Jul 2012, 07:55 pm
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Happy 4th. Sparks and Sparklers but no sparks from my ESL speakers... :nono:
Inspired by reading the recent coffee-table book on QUAD and after a year of thinking about it I figured out how to drive the QUAD 57 from my direct drive amplifer! As QUADAPHILES know that speaker has rather special requirements to both protect it from over voltage (sparking) and is somewhat amplifier fussy. The RM-10 has been popular among QUAD owners and it is widely known that I was using that speaker when I designed the RM-10. Some years later I got a pair of 63's and added some banana jacks on the back so I could direct drive them from a high voltage OTL amp. It's a very easy thing to do and I am willing to post a how to if there are interested parties who have the skills to solder and play safe around high voltages. Actually as long as any ESL is not playing music it is quite safe. The only high voltage that is present at that time is the polarizing and getting shocked by that is only an annoyance, not a danger as it is DC and of low current. It's the high voltage AC from the music that one must not come in contact with. For my pair I installed 4 jacks so I could jumper back in the standard drive electronics easily.
My speaker, the Acoustats and most DIY ESLs are simple 3 wire systems. Those being the front, back and diaphragm wires. There are dozens of articles on how to build your own panels. In fact ESL panels are the easiest speaker to build needing only moderate woodworking skills and easily obtainable materials. By contrast, a magnetic planar or cone driver is almost impossible to build in one's garage shop. The difficulty the DIYer encounters is the drive electronics. The often given solution, reverse connected output transformers being the most popular, is just horrible. Those transformers never have high enough ratio or peak voltage rating. Usually the DIYer finds he has to get a several hundred watt amplifier to get the voltage and then the transformer can't take it. The best solution is the direct-drive amplifier, but those are not for the unskilled to design or make, evidenced that only Acoustat and Beveridge made them and Acoustat quickly converted to a poor sounding substitute transformer box (I worked on one, it's really horrible and doesn't sound nearly as good as a direct drive amp). Acoustat quit making their amp because they wanted wide appeal and their amp was giving them a lot of trouble. Beveridge's amp was better but sat under the speaker making tube replacement difficult. Both were build on circuit boards, which was a bad idea. Both were built at the lowest possible cost as both designers were more concerned with the speaker, not the amplifier. They both had solid state front ends, the Acoustat having an OP AMP. I on the other hand have a lot of concern about amplifier sound and reliability. My amplifier is all tube and has balanced and unbalanced inputs.
The world of ESLs is largely divided into two categories. Here I am just discussing the ESL itself, not considering any cone drivers that may be employed.
1. Full range drivers that have large area and that area produces all frequencies. These tend to be very directional (the Innersound is a prime example) unless they are curved (Martin Logan) or approximated into a curve (Acoustat, Sound Labs). Most DIY designs are full range and either curved or flat, the latter being much easier to build. All are less efficient than multi way as they have high capacitance and will sound very, very bright unless EQ is applied. They all have EQ and this is best applied in DIY situation by a separate graphic EQ which can also correct for the room. This what my customer with the Acoustat Eight (8 panel speaker) does with great success. At 2 KHZ, the response is pulled down 10 dB and the curve is a gentle smile on both ends. This results in flat response in the room. Beveridge and Acoustat both employed EQ in their amps and Beveridge was very particular about his. Many DIY builders do nothing about EQ and have some very strange sounding speakers that could be easily corrected with a descent graphic EQ that can be had for $500. Yamaha and DBX make these both having good sound, balanced XLR output and can drive long lines to the amps that typically sit close to the speakers.
2. This second class of ESL speakers is multi way using panels of different dimensions and often different voltages to obtain line source dispersion. By adjusting the panel size and shape flat response can be obtained without the need for EQ. All the QUAD speakers do this having much larger area for the bass than the treble. The 57 is a 3 way line source where the 63 is a two way point source. I prefer the 57.
The 63 is an easy drive as it is low capacitance (much lower than the Beveridge and Acoustat) and has a single drive voltage. Only 3 wires are needed from the amp to the speaker and test lead wire is quite suitable and safe. The 57 is quite an different issue as it uses two drive and two polarizing voltages which are 1500V for the midrange/tweeter and 6,000 V for the woofer. These are provided in the speaker by the polarizing supply and the audio input (step-up) transformer which is quite complex and contains some crossover components which often go bad. The polarizing supply almost always needs to be replaced if it is original. With my direct drive amp these components can be removed (and sold for good money) as all you need are working panels.
My direct drive system provides both polarizing and audio voltage that will never overdrive the speaker. A common problem with the 57 is that it was intended to be used with the QUAD 22 amplifier which was 15 watts at 16 ohms which turns out to be 30 watts at 8 ohms or a peak of 30 volts which is just what the RM-10 provides, making it the safe choice for standard 57s. People get in trouble with bigger amps as they have higher output voltages. Clamping devices have been created for the 57 but many think they impair the sound of this very clean speaker.
Here is the run-down on what my direct drive amp can do. It can be made at any output voltage and I have a high and low current version because some ESLs draw very high currents due to high capacitance and some don't. This is just the same as the fact that speakers can be 2,4,8,16 ohms and anywhere in between. ESL speakers can be low capacitance, mine are just 100 pf. Beveridge model 2's are 4500 pF. That's a 45 to 1 difference, a much larger range than we see in cone speakers. In addition being capacitive the impedance varies inversely with frequency being lower at higher frequencies. When Beveridge went to transformer drive the result was a speaker that went from 100 ohms at 100 HZ to 1 ohm at 16 KHz. We had to find amplifiers that would deliver over 40 amps of current. These speakers were not suitable for most conventional amps tube or transistor. Roger Sanders makes a solid state mono amp that delivers 2000 watts at a cost of $8000 per pair.
Acoustats are about 300 pF per panel but the good ones have at least 4 panels per side making them 1200 pF. That still puts them in the high range. However if you want to make a small rather directional ESL you can lower that capacitance but a woofer will be required. If there is interest I will direct DIYers to the construction designs I find most appropriate or provide some easy to build suggestions. Acoustat transducers appear to be somewhat available from people who have scrapped the speakers. The panels are almost always good. The problem has always been driving them.
The Quad 57s are only 200 pF and the 63's are low also. In general the ESLs that use full range panels have the highest capacitance and are therefore least efficient. The multi-way ESLs (that means mulit-way in the electrostatics themselves) tend to be low capacitance and much more efficient. The extremes are the QUAD 57 needing 15 watts of drive and the Beveridge needing 1,500. Trumpet music is most demanding. Being a little in disbelief about the 1500 watt number I measured a half amp at 3000 volts. No wonder these speakers can't be driven any other way. The QUAD on the other hand needs the voltage of a 15 watt amplifier (at 16 ohms) but from a 4 ohm tap. In my experience that although the QUAD 22 amp was made to drive the 57 speaker, it was rather rolled off at the top due to the fact that the speaker impedance did fall to about 4 ohms. Not everything QUAD did was exactly as they said, contrary to the rather perfectionist philosophy proposed in the QUAD book.
One nice thing about my direct drive system is that by changing just 2 capacitors in my crossover one can set the brightness of the speaker to his desires either more or less than the standard by as much as 12 dB in either direction. Far more than one would need.
Please respond to the poll so I can get an idea of your interest and have a happy 4th.
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I see plenty of Acoustats selling in the neighborhood of $500.
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please let us know when you do by posting a link.
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I see plenty of Acoustats selling in the neighborhood of $500.
I've been looking on ebay. Where do you see them? Perhaps you could post a link when you seen some.
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You will see them on eBay and AudiogoN with some consistency. I had been looking for a set of ESL or planar speakers for awhile and had a high interest in Acoustat due to low prices. Problem is nobody wants to ship them (somewhat understandable) and most of what I saw was on the East coast. if I see any in the future I will post here.
BTW - I ended up with a pair of Magnepan 1.6QR speakers and may have the Peter Gunn mods done to them. I would still like a set of ESL-57's to pair with my RM-10 though.
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Here are a few listings from Audiogon:
http://app.audiogon.com/listings?utf8=%E2%9C%93&global_search_text=acoustat (http://app.audiogon.com/listings?utf8=%E2%9C%93&global_search_text=acoustat)
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Sometimes I look at the Electronic Shopper.
http://www.theelectronicsshopper.com/
the best place is Craigslist but use the Searth Tempest. Try this url. If it works, you will see a lot.
http://www.searchtempest.com/results.php?location=65622&maxDist=50000®ion_us=1&search_string=acoustat&keytype=adv&Region=na&cityselect=zip&page=0&showeb=1&category=8&subcat=sss&minAsk=min&maxAsk=max
Here is a pair of Model 3's for $600 in Fontana Ca.
http://orangecounty.craigslist.org/ele/3073540209.html
It looks like many are in Ca.
Also, I signed up for Oodle Alert, that helps.
I also look here sometimes. They use to have Craiglook.
http://claz.org/
Here is a pair of 4's in Aurora Co. for $800 including a Yamaha reciever.
http://www.reachoo.com/ads/56569135#denver-Nice%20Acoustat%20speakers%20and%20receiver%20(aurora)
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Here is a pair of 4's listed in Memphis for $500.
http://memphis.craigslist.org/ele/3099574973.html
What is funny about this ad, they list the transformers as mono amps.
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And on Ebay, here is a pair of the 6's in Northridge Ca. for $1800 or best offer.
http://www.ebay.com/itm/ACOUSTAT-6-WITH-4-MEDALLION-TRANSFORMERS-/230813991918?pt=Vintage_Electronics_R2&hash=item35bd9603ee
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As I wrote on a different thread, I have Stax F83's driven by NYAL OTL3's. I think the sound is glorious (and yes, including, maybe
especially, trumpets, despite the drop in impedance of these speakers at high frequencies). I only buy equipment when necessary,
eg I bought Roger's great subwoofers because I was having serious bass distortion, and I recently replaced by 30 year old van den Hul cartridge with another van den Hul (just one step up). If the transformers of the Stax's die (not unheard of, unfortunately), or if the amps die and can't be repaired, and if the DD amps aren't too pricy, then I would certainly consider them. I wonder though if it is okay to have them at the other end of the room, with a long speaker cable? Also, it seems to me that it would be a good idea to have some sort of box to cover the speaker terminals. Even with my Futterman's I once got a painful shock from the amps while music is playing when I touched the leads. Couldn't the DD amp be fatal under such circumstances?
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I sold Acoustat and NYAL back in the 80's. I received a pair of the Acoustat Minitors with DD amps on trade. It was a night and day difference between the DD amps and the NYAL 3's, no contest. The DD amps blew the Futterman's away.
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I wouldn't be surprised if the DD is much better. Didn't Roger say above in particular that the transformers Accoustat used were not good?
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As I wrote on a different thread, I have Stax F83's driven by NYAL OTL3's. I think the sound is glorious (and yes, including, maybe
especially, trumpets, despite the drop in impedance of these speakers at high frequencies). I only buy equipment when necessary,
eg I bought Roger's great subwoofers because I was having serious bass distortion, and I recently replaced by 30 year old van den Hul cartridge with another van den Hul (just one step up). If the transformers of the Stax's die (not unheard of, unfortunately), or if the amps die and can't be repaired, and if the DD amps aren't too pricy, then I would certainly consider them. I wonder though if it is okay to have them at the other end of the room, with a long speaker cable? Also, it seems to me that it would be a good idea to have some sort of box to cover the speaker terminals. Even with my Futterman's I once got a painful shock from the amps while music is playing when I touched the leads. Couldn't the DD amp be fatal under such circumstances?
The Direct drive amps should be relatively near the speakers as long cables will add capacitance, which is the one thing we want to minimize. To keep cost down I am planning a stereo version with 8 output tubes and 6 drive tubes on an RM-200 chassis. I plan to set mine between the speakers with a 6 foot run to each. The connectors are in-line and shock proof. The cables are covered with the typical plastic braid we see so often on speaker cables. Tentative price for a stereo amp is $4500. The monoblocs $8000 per pair.
I am also making monoblocks which I have set behind my speakers but it seems a shame to have them hidden when they could look so nice in front. No matter where my equipment rack sits, I always like to put the amp on a small stand between the speakers.
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I sold Acoustat and NYAL back in the 80's. I received a pair of the Acoustat Minitors with DD amps on trade. It was a night and day difference between the DD amps and the NYAL 3's, no contest. The DD amps blew the Futterman's away.
Thanks for report on an excellent comparison. Here are a few contributing factors. If played loud the Futtermans have not the current needed to drive Acoustats, especially ones 3 panels or larger. The impedance of any large, full range panel speaker is going to approach 1 or 2 ohms at high frequencies and Futterman amps put out nothing into 1 ohm nor do the tubes appreciate the task.
It is a long standing myth that OTL amps and ESL speakers were made for each other. This is true in one combination, the Futterman OTL and the KLH-9 which was a 16 ohm speaker that stayed pretty constant over the range. I have a copy of Julius Futterman's impedance measurements in my "Futterman File". He was certainly interested in driving this speaker as he measured its impedance at over 20 different frequencies. The advantage of his amp over others was it had lots of voltage which the KLH-9 needed. I am told that one of the classic listening tests was to compare the Futterman vs the Marantz 9 driving the KLH, particularly on Saturdays at Lyric Hi FI, NYC.
A Futterman can drive the QUADs or the Stax that airhead has but one has to be very careful not to exceed the maximum voltage which is 35 volts peak for the QUAD 57's and about 40 volts peak (100 watts from a 8 ohm amp) for the 63's. I do not know what the peak is for the Stax. I do know that most Futterman amps can put out 150 volts peak and therein lies the danger.
When Acoustat gave up on making their "Servo Amplifier" they went to a two transformer system, a system that is flawed in its very nature,. There is really no way to drive a single panel ESL with two transformers one being for the lows and one for the highs. One can split the band on the input side but they have to re-combine the bands on the output side and that causes the high frequency transformer to "see" enough of the low frequency information to cause saturation at higher levels and significant 3rd harmonic distortion at moderate levels. Although I don't have my measurements of the Acoustat Magnetic Interface handy, I do recall it is not easy to drive. It needs lots of voltage and lots of current.
Although rarely mentioned, the transformers in ESL speakers often eat up 25 to 50% of the drive energy due to their capacitance at the high end and saturation at the low end. When we eliminate them and the output transformer in a traditional amp and connect the tubes directly to the panels there is a great relief of work that the tube have to perform.
As you can see, from both a safety and sonic perspective, direct drive makes a lot of sense. When you can go directly to the panels, an ESL is actually easier to drive than a magnetic speaker.
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I tried many amps back then, since I sold Acoustat. I even made it to the top 5 in sales in 1982-83. I was very proud of that.
The Acoustat twin Nova amp was actually one of the best to drive them, although it did not sound the best. I tried NYAL Futtermans, David Berning, Conrad Johnson, Qucksilver, Rowland, Threshold, Belles, Sumo...... the list was very long. The worst combination was the tube amps with output transformers. Just way to many transformers in the system, it sounded very sluggish and veiled.
But when I hooked those Monitor 3's with DD amps up, voila! About 3-4 layers of veil was lifted. And I was very surpised of the bass response, much deeper and faster.
With the $4500 price tag for the stereo amp and a used pair of Acoustats at about $500, this is a steal in today's market of ultra high-end audio. $8500 isn't too bad either.
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What we need is a kit to accompany the new amp. Building ESL panels can be relatively easy. Sourcing parts definitely isn't. Instead of buying used antique Accoustat panels, with their rather thick and heavy panels & membranes, a simple panel can be designed with precut insulated perf-metal sheets, some copper foil, a suitable Mylar (the tricky part) diaphragm, and quality double stick tape. With the right supplies this should be a one day project. Especially if flat panels are desired. Roger's, amp would make all of the related transformers and bias supply, and their related headaches, unnecessary. If you desire lots of volume, a woofer and crossover would be required. Done right, it could be easier than assembling a backyard swing set.
steve
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What we need is a kit to accompany the new amp. Building ESL panels can be relatively easy. Sourcing parts definitely isn't. Instead of buying used antique Accoustat panels, with their rather thick and heavy panels & membranes, a simple panel can be designed with precut insulated perf-metal sheets, some copper foil, a suitable Mylar (the tricky part) diaphragm, and quality double stick tape. With the right supplies this should be a one day project. Especially if flat panels are desired. Roger's, amp would make all of the related transformers and bias supply, and their related headaches, unnecessary. If you desire lots of volume, a woofer and crossover would be required. Done right, it could be easier than assembling a backyard swing set.
steve
The Acoustat Monitor 3's and 4's played with a lot of bass and volume without any subs. As long as you used Acoustat's DD OTL tube amps and not the transformers.
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Tom,
I remember them well. I recently, well last year anyway, heard a pair of "X's" that were still working after all these years. I just wonder if rehab jobs of their other speakers are worth the effort. Materials today are better.
I'm also a member of the " hybrid is preferred" club.
Steve
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I'm also a member of the " hybrid is preferred" club.
Steve
Are you taling about hybrid amps, Steve? Of the Acoustats with transformers, the Moscode 300 and 600 amps sounded the best back then.
If I would run ESL's today that had transformers, the Moscode 401HR by George Kaye would probably be at the top of my list. I would still prefer DD amps no matter what ESL it was.
But you are probably talking about hybrid speaker system. I have always preferred full range. I have never heard a sub as quick as ESL's.
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It took me a long time to accept the idea that I should use subwoofers with my Stax F83's. They did have satisfying fast, tight, dry bass which could be impressive. But after getting them fixed, I noticed there was some distortion with ultra low (not necessarily loud) notes, and decided probably the Futtermans weren't deliver the current the speakers needed. Therefore I got a pair of Roger's subs. This solved the problem, but they sounded so different that I wasn't sure at first I liked them. I eventually realized that, unlike the stax's one-note resonance induced bass, they were actually playing tunefully in the low registers, with a sort of bloom and musicality that had been lacking. This is not like the big thumps that make people go "wow" when they hear most dynamic woofers, and, although not super loud, quite fast and realistic. Nothing is perfect, but I think that, even apart from the distortion issue I was occasionally hearing, there is a big improvement. Plus I feel much safer at higher volumes.
By the way, the impedance of the Stax's ranges from 4.5 ohms at the frequency extremes to about 160 ohms in the midrange. I don't think the Futtermans have any trouble at all with the 4.5 ohms at the highest frequencies. They are very inefficient, and need lots of voltage, hence the Futtermans. Probably its true that the AR D250 made was the worst sounding combination among those I tried (years ago).
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I have a pair of the Monitor IV's Tom is referring to with the DD amps that have been rebuilt by a gentleman in Oklahoma City. Absolutely no comparison to an amp running through transformers to the same panels. Bass is tighter, that slight 'plasticy' (technical term...) sound isn't there. MUCH faster and more dynamic.
Picked them up along with an AR preamp, Nakamichi tape deck, Sony CD player, and Yamaha tuner for $600 on Craigslist. Sold pretty much all of the rest of it and basically have zero in the speakers before I paid for the amp rebuild/mods. One of the best buys I've ever made in my audio journey.
Bryan
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I have a pair of the Monitor IV's Tom is referring to with the DD amps that have been rebuilt by a gentleman in Oklahoma City. Absolutely no comparison to an amp running through transformers to the same panels. Bass is tighter, that slight 'plasticy' (technical term...) sound isn't there. MUCH faster and more dynamic.
Picked them up along with an AR preamp, Nakamichi tape deck, Sony CD player, and Yamaha tuner for $600 on Craigslist. Sold pretty much all of the rest of it and basically have zero in the speakers before I paid for the amp rebuild/mods. One of the best buys I've ever made in my audio journey.
Bryan
And I have really missed those Monitor IV's ever since. I sold those to Bryan about 30 years ago.
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I owned Acoustat Spectra 33’s for many years. Those speakers drove me crazy. They had so much potential, yet, always found them difficult to coax out the best from them. The amp choice was always difficult to find a good match. For me, the Audio Research D115 was the best match I found for it. Also, used an Infinity Servo subwoofer with them, which did help the overall sound (the Acoustat woofer designed to those was sorely lacking).
These days, I find the SEAS Excel drivers provide speed and detail much like a ESL, and provides dynamic contrasts most ESL’s just cannot each. Still, ESL’s will always hold a special place in my audio journey, and are always a welcome sonic experience.
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I owned Acoustat Spectra 33’s for many years. Those speakers drove me crazy. They had so much potential, yet, always found them difficult to coax out the best from them. The amp choice was always difficult to find a good match. For me, the Audio Research D115 was the best match I found for it. Also, used an Infinity Servo subwoofer with them, which did help the overall sound (the Acoustat woofer designed to those was sorely lacking).
These days, I find the SEAS Excel drivers provide speed and detail much like a ESL, and provides dynamic contrasts most ESL’s just cannot each. Still, ESL’s will always hold a special place in my audio journey, and are always a welcome sonic experience.
I am afraid with any ESL's, there is only one way to listen. Get rid of the transformers and use DD amps. It is truly a night and day difference. When you hear the differnce, it will shock you. Transformers really makes an ESL sound very sluggish.
I am hoping all ESL owners start realizing what Roger is designing here. This would definitely be a game changer in the ESL audio world. There have been many, many thousands of Acoustats and Quads that have been sold over the past 35-55 years.
Oops! :duh:
Roger, can you make that many amps?
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Agreed that the best way to power ESL's is to drive them directly.
But... For best full range performance, a dynamic woofer is necessary.
This new amp could be a very big seller.
Addendum: I just got took to task by a buddy who prefers solid state power. He insists that a transformer coupled ESL driven by a bipolar solid state amp is more accurate, distortion free, than a direct drive tube amp. He did agree that not having a transformer in the speaker made for an easier design, especially for hobbyists. I questioned that since an ESL is such a difficult load, a good policy would be to design a specific use amp, and avoid generic product. This discussion has the potential to go on endlessly as there are too many variables to compare.
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But... For best full range performance, a dynamic woofer is necessary.
You should listen to the IV's. The resonant frequency of the panels is 23Hz I believe. They have no problem at all going to and below 30Hz when required. One of the things I love about full range panels is the bottom end. It's just so much tighter, cleaner, faster, more detailed, more 'musical'. Trying to get a dynamic woofer to keep up with a panel is pretty tough to do unless you do an OB or IB type.
Bryan
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Agreed that the best way to power ESL's is to drive them directly.
But... For best full range performance, a dynamic woofer is necessary.
This new amp could be a very big seller.
Addendum: I just got took to task by a buddy who prefers solid state power. He insists that a transformer coupled ESL driven by a bipolar solid state amp is more accurate, distortion free, than a direct drive tube amp. He did agree that not having a transformer in the speaker made for an easier design, especially for hobbyists. I questioned that since an ESL is such a difficult load, a good policy would be to design a specific use amp, and avoid generic product. This discussion has the potential to go on endlessly as there are too many variables to compare.
I would ask your buddy what direct drive amplifier he is comparing his solid state+transformer to? I have seen many DD amp designs that are just horrible. For those he might be right. You might also tell him that I totally disagree about the distortion as the transformer is out of the loop. Also let him know that the transformer capacitance often eats up 1/3 to 1/2 the power of his SS amp.
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Wow! Roger, what a great thread. ESL's sound pretty fantastic anyway, but I gotta say the thought of pitching the trannys and driving my homebuilts directly really has me intrigued. Not sure I could afford the amps, even if sold as kits, but I sure like the thought.
BTW, if everyone knew how easy it is to roll your own ESL's (flat panels especially), I think there would be a lot more ESL owners here.
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I'll happily provide a pair of Quad 57's if you want a beta tester!
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I remember back in the early 80's, Frank Van Alstine said that the Acoustats with DD amps made all other ESL's sound broken.
It is too bad that Acoustat got greedy and went mid-fi with their speakers to sell more to the general public.
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I remember back in the early 80's, Frank Van Alstine said that the Acoustats with DD amps made all other ESL's sound broken.
It is too bad that Acoustat got greedy and went mid-fi with their speakers to sell more to the general public.
Frank was right about that. The sound was certainly better and much much better than with the transformer box that replaced the DD amp.
Besides being more expensive than the transformer they later provided, I believe that Acoustat abandoned the DD amp because their's was not reliable.... at all. They had a plug in cathode resistor which failed often (hense the plug in). They also built the sockets out of indivdual pins on a PC board which didn't hold the tubes tight and for some reason used the smallest of the horizontal output tubes available, without a plate cap no less. The front end was a TL-074 and some transistors to drive the tube. It was more like a High Voltage power supply design than an audio amplifier.
I have opted for the larger tubes, with plate caps which gets the high voltage away from the low. Also mine is all hardwired, real tube sockets screwed to the chassis and a reliable circuit (of course).
I think Acoustat realized early on that the amp was a big problem and would inhibit both the production and reliability of the broad line of speakers they produced over time. Even before the Spectra series there was every possible combination of panels from one to eight. Now we can buy these speakers at incredibly low prices and drive them properly.
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If anyone here is in Chicago area, this deal is a steal on Acoustats with DD amps on Ebay. The seller first listed them at $1500, then $1200, now $900. Only if Chicago wasn't so far away. :(
Hey Brian, how about going up there and picking these up for me?
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=130726826241
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I live in a Chicago suburb.
We are talking just a few miles away.
Steve
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I live in a Chicago suburb.
We are talking just a few miles away.
Steve
The speakers are in Bellwood, Il. They look like they are in very nice condition.
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Perhaps I should add to this thread the fact that Harvey Rosenberg was toying with the idea
of a Futterman-Stax dedicated combination, which I imagine would have been direct drive.
He never implemented it though.
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Naturally the guy who lives closest to the speakers (Riverside, IL) doesn't want them. I'm way too much of a DIY speaker kind of guy. I would be willing to store those speakers for another forum member for a few months until he could make pick up arrangements though. Seriously.
Steve
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Maybe I'll buy them so I can do surround sound Acoustats! Somehow, I don't think my wife would think that's a great idea.... :nono:
Bryan
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Would someone knowlegeable about that acoustat deal PM me and tell me why this is a good deal? I was just looking at Magnepans... so not sure what these are. (--planar Newb) I live near them.
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:o
Wow, what a deal this was in Canada last April. A free pair of Acoustat X's and DD amps if you picked them up at his place.
http://www.canuckaudiomart.com/details/648994386-acoustat_x_speakers_servocharge_amps_conradjohnson_preamp/
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:o
Wow, what a deal this was in Canada last April. A free pair of Acoustat X's and DD amps if you picked them up at his place.
http://www.canuckaudiomart.com/details/648994386-acoustat_x_speakers_servocharge_amps_conradjohnson_preamp/
That was a great deal. Sometime people do give things away and because they are giving them away others may not realize that they are of great value. I hope I have alerted those reading this thread what you are missing in fooling around with Electrostats.
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Would someone knowlegeable about that acoustat deal PM me and tell me why this is a good deal? I was just looking at Magnepans... so not sure what these are. (--planar Newb) I live near them.
Magnepans attempt to do what ESLs do but with a diaphragm that is 10 times more massive in a non-linear magnetic field. Their one virtue is that they are planar and that is all they share with ESLs.
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:o
Wow, what a deal this was in Canada last April. A free pair of Acoustat X's and DD amps if you picked them up at his place.
http://www.canuckaudiomart.com/details/648994386-acoustat_x_speakers_servocharge_amps_conradjohnson_preamp/
Ouch, I am in the same city but never follow Canuck Audio Mart. :roll:
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Traderxfan,
Roger gave a great explanation of the differences between ESL, and Magnepans. If you get the chance to listen to both, you will notice that ESL's do not ring, overshoots, or exhibit any tonal imbalances. Magnepans are driven from one side only so that there is kind of a "snap-blur" effect. The diaphragm has to restore itself after the signal drive. I would love to see some 'scope pictures comparing them reproducing sine waves.
Steve
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Thanks for the comments above, and OzarkTom's who pm'd.
I wasn't so much weighing the pros and cons of magnepan vs acoustats. I just didn't have a clue about Acoustats. And more specifically, what made this deal so special, since it is in my backyard. I was skeptical because it seemed just to be old and defunct technology.
After doing some Google research about Acoustats. I read about some of the tradeoffs. The only one of which that gives me pause is a few comments mention rolled off treble. Is that your experience?
I was expecting the complete opposite for the treble. I have a few different speakers here. The one that I have that most closely might give me an approximation to the design aspects of this would be my GR Research OB-7, paired with four 12" ob servo sub drivers. The relatively extended highs form the B&G neo3 tweeters are one of the strengths I was looking for when I started thinking about a full planar speaker.
But in regards to the line source aspect, and the crossover-less design, I have no approximation or experience with that.
-Tony
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Any rolloff is in the extreme high end. They are very particular about listening height though. If you stand up, yes, you lose the highs somewhat. The Monitor IV's have an adjustment on the rear so the entire panel can be tipped back slightly to help avoid this problem and dial it in to your preference.
The stock DD amps are head and shoulders above the transformers. I had mine completely rebuilt and some pretty serious mods done to them which really take them to a whole different level.
Bryan
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The Acoustats with transformers had the worst roll-off in the top in. I loved the top end with DD amps. I have never heard GR OB-7, only the GR Super V's. If you like that top end, you will like Acoustats top end. IMO, all ribbon tweeters have always sounded to hot for me.
But like Byan said, stay seated to get the best results. This is not a dance speaker.
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You might email that seller, TRADERXFAN, and he might will let you come over and listen before the auction ends. But the amps will sound much more open and clearer if they are modified.
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I didn't want to start another topic but I have a comment and also a question.
Earlier Roger (When I wrote that a buddy felt direct drive tube amps were inferior to solid state amps powering ESL amps through transformers) commented that the condition of direct drive amps not working well would be if they were ill-conceived DIY units. That is exactly the case. Martin Logan statements driven by Bryston amps verses a homebuilt DD tube amp driving Acoustat 1+1's converted to direct drive. Not a fair comparison at all.
My question to the group is since we are talking dipole speakers, how about Heil drivers? Not the offshore tweeters but the rereleased Great Heils. I just finished restoring an original pair from old ESS AMT-1's. Combined with a decent corner horn, I am impressed. What is your experience with these drivers? Of course compared to ESL's.
Steve
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I always tried to like the ESS's when first they came out, but the highs were just too bright. I also thought the bass was too boomy. When I visited the Heil room at RMAF last October, I just barely went into the room and quickly out. The brightness almost fried my ears and gave me a headache. But maybe there is an amp today that can tame that down.
I had a friend that used highly modified Heil tweeters in his system, almost sounding smooth.
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The bass in the original was boomy. I only kept the Heil cores, and cleaned them up, put in new diaphragms. I don't feel they are too bright. Perhaps amp choice makes a difference. Or maybe they are driving the tweeter several DB louder than the woofer. In my live hardwood floor room they sound okay.
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I sold Acoustat and NYAL back in the 80's. I received a pair of the Acoustat Minitors with DD amps on trade. It was a night and day difference between the DD amps and the NYAL 3's, no contest. The DD amps blew the Futterman's away.
A further bit of information on the Acoustat + Futterman combination, the following quote from Harvey Rosenberg:
"On the other hand musicmaniacs would here these amps on Quad 63s and then used them on their Acoustat Monitors, where were very inefficient, 2 ohm speakers…which I advised against…and then I would get a call from and OTL-3 owner complaining that after only two months his amplifiers sounded distorted. As I suspected the output tubes were exhausted, and for good reason.The rumors started by the mealy minded that the Futterman amplifiers were unreliable arose because these thermionic feeble never understood that OTL amplifiers can only be used with a very limited range of loudspeakers…and be reliable."
The link is here… http://www.meta-gizmo.net/tri/nyal/nyal_art.html
I should add that my OTL 3's have been very reliable with long tube life, except for the time one of the caught fire....
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One must remember that OTL amps like the Futterman and Atmasphere are current limited and thus put out decreasing power into lower loads. In approximate numbers you can get 1 to 1.5 amps per pair of tubes so 3 pairs in the OTL-3 would do 3 to 4.5 amps, about right for 100 watts into 8 ohms. Divide that in half for 4 ohms and half again for 2 ohms. As to burning up the tubes, that is correct because the voltage that is not appearing across the load is not across the tubes thus taking their dissipation far beyond rating.
It should also be noted that in some ESL step-up transformers half the total capacitance is in the transformer itself. Direct drive removes this undesirable load. The Quads work out to about 200 pf with my crossover which is quite easy to drive at high frequencies. Acoustat panels are about 300 pf each. In the larger speakers this does add up but I make a higher current amp for those. The big one I am making for a customer drives 8 panels that's 2400 pf. We made some measurements and found that with that much area, even in a very large room, half the original Acoustat voltage was plenty for extreme levels. Therefore I made a lower voltage, higher idle current (more class A) amp for him.
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Those Acoustat X's on Ebay went for $910. Did anyoe here get those?
And here is a pair of Acoustats in Ramona Ca. for $500. These even have the original boxes and owner's manual.
http://sandiego.craigslist.org/csd/ele/3134944198.html
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Hi
I just came upon his thread. I would be very interested in seeing the schematics from Roger. I am in the middle of rebuilding some Acoustat Monitor 4 using 4 x 9" panels /channel. I have a MK-121 interface to drive them but would be very interested in direct drive amplifiers for them. There was also a circuit designed by Alan Kimmell for direct driving electrostatic speakers it has 8 x 6HV5 tubes /channel and was offered by David Lucas at one time but I have never seen any more info on the net about the amps.
Andrew
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Hi
I just came upon his thread. I would be very interested in seeing the schematics from Roger. I am in the middle of rebuilding some Acoustat Monitor 4 using 4 x 9" panels /channel. I have a MK-121 interface to drive them but would be very interested in direct drive amplifiers for them. There was also a circuit designed by Alan Kimmell for direct driving electrostatic speakers it has 8 x 6HV5 tubes /channel and was offered by David Lucas at one time but I have never seen any more info on the net about the amps.
Andrew
Does anyone know where David Lucas is? I had a bad experience with him and I hear others did also.
I would be interested in seeing the 6HV5 design,though I wouldn't use that tube. It was designed to be a pulse type shunt regulator in a color TV and it's linearity is not so good. From a reliability point of view its better to have a plate cap for the high voltage, which the 6HV5 doesn't.
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Roger,
A fellow named Dan Fanny, formerly of American Hybrid Technology in Trenton NJ, rebuilt Acoustat DD amps. He had boards made of his design. He used cap tubes which were an upgrade from horizontal stabilizer? (prob 6HV5) TV tubes. I believe the only thing original was the power transformer and any storage cap that was still good. I had a pr of these amps, they were astounding. He used all different kinds of high voltage storage caps. I remember stringing together banks of 250V photo-flash caps to make 50KV with relatively high current. They packed a wallop.
Danny had 2 +2 panels, The sound was effortless. I'm not sure how many sets of these amps are floating around, they didn't all have photo-flash caps, but I think they would be worth checking out. The tubes last quite a long time. When you wrote about biasing tubes, you reminded me of Danny. He told me that when it comes to biasing and matching, nobody knew what they were doing. The tubes in my conventional 50 wpc amp, were good for around 10 yrs.
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Question for Roger.
How are the direct drive ESL amps coming along? Anything new to discuss?
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Bump
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A friend of mine in Maine has a pair of Acoustat 3's for $450! He has them listed at Boston Craigslist. At my urging he picked up today a pair of Monitor 4's in their original boxes for $500!
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A friend of mine in Maine has a pair of Acoustat 3's for $450! He has them listed at Boston Craigslist. At my urging he picked up today a pair of Monitor 4's in their original boxes for $500!
:o
With the servo amps?
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Yes with Servo amps.
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What we need is a kit to accompany the new amp. Building ESL panels can be relatively easy. Sourcing parts definitely isn't. Instead of buying used antique Accoustat panels, with their rather thick and heavy panels & membranes, a simple panel can be designed with precut insulated perf-metal sheets, some copper foil, a suitable Mylar (the tricky part) diaphragm, and quality double stick tape. With the right supplies this should be a one day project. Especially if flat panels are desired. Roger's, amp would make all of the related transformers and bias supply, and their related headaches, unnecessary. If you desire lots of volume, a woofer and crossover would be required. Done right, it could be easier than assembling a backyard swing set.
steve
I could make such a kit available. I do have heat shrink mylar available now for those who want that. Currently I am still a fan of the Acoustat method of using the plastic light grill as a stator with wires attached. However this is a bit difficult for the hobbyist as there is significant tooling and jigs required to stretch and glue the wires. I have a 30% less deep light grid and a very good tubular aluminum frame to go around my panel and stiffen the grid at 1 foot intervals.
Perf metal sheets are popular though they need to be put in a rigid frame and perf metal is actually rather expensive. (perhaps someone knows a source better than Harrington and King). Then there is the coating which has to be done and tested for possible arcing spots which have to be touched up.
All things considered, I still recommend the Acoustat panel for its low cost and availability.
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Now taking orders for the stereo direct drive amps for Acoustat to be delivered early 2013 or sooner. In a black metal chassis the price is $4,000. I will also make available a unit in the RM-200 style with wood base at $4,800. A $1,000 deposit will secure your order. Please write ramtubes@gmail.com if you are interested.
The amps will drive up to 4 panels per side and supply 5 KV polarizing. You can then sell the transformers as you no longer need them. Connection is via three banana jacks directly to the 3 wire panels. Chassis are plain black aluminum, balanced XLR or RCA input. EQ must be provided by the user and I suggest a 30 band analog EQ from Yamaha Q2031B or DBX 1231 as it will do a better job than the EQ that is in the transformer box and allow you to correct for room and personal taste. We have listened to these units and found them to be quite neutral.
The mono amps will drive up to 8 panels per side and sell for $8,000 per pair.
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Perf metal sheets are popular though they need to be put in a rigid frame and perf metal is actually rather expensive. (perhaps someone knows a source better than Harrington and King). Then there is the coating which has to be done and tested for possible arcing spots which have to be touched up.
All things considered, I still recommend the Acoustat panel for its low cost and availability.
OnlineMetals.com sells precut steel perf pretty cheap: .036 x 12 x 48 / 40% open / .125 holes @ $20 each, and you can order custom sizes.
I would love to try my hand at building the insulated wire / light diffuser stators you described, and if you have any build photos, I would love to see them.
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Hi Roger
Is the EQ required to generally counter a rising response with frequency and therefore could this be achieved by progressive reduction of panel area driven with increasing frequency ala spectra versions of acoustats? Understand that this would not be easy to achieve and that the equalisers you describe would both simplify the iterative process and provide greater flexibility to address the other issues you describe.
Regards
Grantn
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OnlineMetals.com sells precut steel perf pretty cheap: .036 x 12 x 48 / 40% open / .125 holes @ $20 each, and you can order custom sizes.
I would love to try my hand at building the insulated wire / light diffuser stators you described, and if you have any build photos, I would love to see them.
Thanks for the suggestion. I encourage those interested in making their own panels to visit Jazzman's site. I have found his methods to be very practical and thoroughly explained. http://jazzman-esl-page.blogspot.com/2010/01/building-stat-panels.html
I would also suggest this one http://www.onlinemetals.com/merchant.cfm?pid=13500&step=4&id=1003&top_cat=0. It is 1/8 " thick. One might go to the 1/4 inch hole size. If you use the steel that's only .036 that is pretty thin and would need some bracing internal and external to maintain a constant gap.
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We have now delivered five direct drive amplifiers to Acoustat users. We also sold one user 8 panels to build his own speakers. We are accepting orders for the stereo unit at $4500 and the mono pair for $8000.
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Thanks for the suggestion. I encourage those interested in making their own panels to visit Jazzman's site. I have found his methods to be very practical and thoroughly explained. http://jazzman-esl-page.blogspot.com/2010/01/building-stat-panels.html
I would also suggest this one http://www.onlinemetals.com/merchant.cfm?pid=13500&step=4&id=1003&top_cat=0. It is 1/8 " thick. One might go to the 1/4 inch hole size. If you use the steel that's only .036 that is pretty thin and would need some bracing internal and external to maintain a constant gap.
Good point. My preference for perf metal stators is 18-gauge (.048") with 1/8" max hole size, which gives very good efficiency. Online Metals does not offer a suitable perf in that thickness, but I've found that their 20-gauge (.036") perf works just fine for 12" wide panels with 2 center-support spacers; especially if you bond on a couple of steel bars for mass and support as shown in the photos below. The photos actually show a panel made with even thinner .030" steel perf, 51% open with .117 diameter holes (very efficient!)--- with a couple of 1/2" square iron bars bonded to the rear stator for strength and dampening. The square bar stock is precut 1/2" x 48" purchased from Home Depot ($6 each). The added steel bars work very well for damping vibrations.
Curved panels can use thinner perf but the .036" perf from Online Metals works OK for 12" wide flat panels. I would not go thinner than .036 for flat panels. As is always the case with metal perf stators, flatness is an issue and you can't count on any perf being perfectly flat... so I also advise using short spans between the center support spacers to accommodate stators that aren't perfectly flat. Sanders' Cookbook recommends setting the span between support spacers at 70-100 x d/s (diaphragm/stator spacing) but I recommend closer to 70 than 100 for the reasons just stated. :thumb:
(http://1.bp.blogspot.com/-8xe7LiI7MQo/UmcPZLmCX5I/AAAAAAAAAxg/5ajbTsBJa8g/s1600/009.JPG)
(http://1.bp.blogspot.com/-TLO2X3HoI7E/UmcPolZRueI/AAAAAAAAAxo/nUsdEeiXrJc/s1600/007.JPG)
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Good point. My preference for perf metal stators is 18-gauge (.048") with 1/8" max hole size, which gives very good efficiency. Online Metals does not offer a suitable perf in that thickness, but I've found that their 20-gauge (.036") perf works just fine for 12" wide panels with 2 center-support spacers; especially if you bond on a couple of steel bars for mass and support as shown in the photos below. The photos actually show a panel made with even thinner .030" steel perf, 51% open with .117 diameter holes (very efficient!)--- with a couple of 1/2" square iron bars bonded to the rear stator for strength and dampening. The square bar stock is precut 1/2" x 48" purchased from Home Depot ($6 each). The added steel bars work very well for damping vibrations.
Curved panels can use thinner perf but the .036" perf from Online Metals works OK for 12" wide flat panels. I would not go thinner than .036 for flat panels. As is always the case with metal perf stators, flatness is an issue and you can't count on any perf being perfectly flat... so I also advise using short spans between the center support spacers to accommodate stators that aren't perfectly flat. Sanders' Cookbook recommends setting the span between support spacers at 70-100 x d/s (diaphragm/stator spacing) but I recommend closer to 70 than 100 for the reasons just stated. :thumb:
(http://1.bp.blogspot.com/-8xe7LiI7MQo/UmcPZLmCX5I/AAAAAAAAAxg/5ajbTsBJa8g/s1600/009.JPG)
(http://1.bp.blogspot.com/-TLO2X3HoI7E/UmcPolZRueI/AAAAAAAAAxo/nUsdEeiXrJc/s1600/007.JPG)
nice panels Jazzman. Do you have some capacitance measurements? What is your typical diaphragm to stator spacing and polarizing voltage? I have found that lower distortion at high levels is obtained when the polarizing voltage is half the voltage that produces noise in the panel. Although some say to put the polarizing right below the noise value but then the noise is occurring on peak signal though it is covered up by the music. Reducing the polarizing really cleans things up at high levels.
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I bought a pair of Model 3 Acoustats a few months ago and now have the parts to upgrade the caps and resistors to upgrade the interfaces. This direct drive topic is interesting, BUT I can't afford this $4500 amp. Is there a make and model DD amp that is affordable and will do the job that I could look for on the used market?
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I bought a pair of Model 3 Acoustats a few months ago and now have the parts to upgrade the caps and resistors to upgrade the interfaces. This direct drive topic is interesting, BUT I can't afford this $4500 amp. Is there a make and model DD amp that is affordable and will do the job that I could look for on the used market?
DD amps are rare, only Beveridge and Acoustat made them. You can buy a pair of used Acoustat amps for around $2000. If you have trouble with them I can fix them. The Beveridge is only suited to his speaker.
Don't bother upgrading the parts in the interfaces, it won't make much difference. The problems are in the concept not the parts.
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I bought a pair of Model 3 Acoustats a few months ago and now have the parts to upgrade the caps and resistors to upgrade the interfaces. This direct drive topic is interesting, BUT I can't afford this $4500 amp. Is there a make and model DD amp that is affordable and will do the job that I could look for on the used market?
I have seen some Acoustat DD amps sell on Craigslist for as low as $500 for the pair. It is a night and day difference between the DD amps and the interfaces. 100K amps cannot make the interfaces sound near as good.